Chapter 6 The Structure Of Living Organisms Long Answer Type Questions
Question 1. Name the characteristics of living things. What is the law of biogenesis?
Answer:
The Seven Characteristics of Living Things
1. Feeding: All living organisms need to take substances from their environment to obtain energy, grow and stay healthy.
2. Movement: All living organisms show the movement of one kind or another. All living organisms have internal movement, which means that they have the ability to move substances from one part of their body to another.
Some living organisms show external movement as well—they can move from place to place by walking, flying or swimming.
3. Breathing or Respiration: All living things exchange gases with their environment. Animals take in oxygen and breathe out carbon dioxide.
4. Excretion: Excretion is the removal of waste from the body. If this waste is allowed to remain in the body it could be poisonous.
Humans produce liquid waste called urine. We also excrete waste when we breathe out. All living things need to remove waste from their bodies.
Growth: When living things feed they gain energy. Some of this energy is used for growth. Living things become larger and more complicated as they grow.
Sensitivity: Living things react to changes around them. We react to touch, light, heat, cold and sound, as do other living things.
Reproduction: All living things produce young. Humans make babies, cats produce kittens and pigeons lay eggs. Plants also reproduce. Many make seeds which can germinate and grow into new plants.
Living beings reproduce to form young ones that resemble their parents in the long run. So it is ‘like from like’- referred to as Answer: the law of biogenesis.
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Question 2. What is a cell? Who coined the term? How it can be seen?
Answer:
Differences Among Living And Non-Living
An attempt should now be made to distinguish living things from lifeless nonliving or inanimate objects. There is no difficulty in recognising a coconut palm or guinea pig as living objects and rocks in the field or the sand grains in the seashore as non-living bodies.
It may be mentioned here that viruses are an intermediate stage between living and nonliving forms of matter.
The principal points of difference between living and nonliving objects are described in tabular form below:
| Living | Non-living | ||
| 1 | Each kind of plant and animal has a definite form and size, which may vary within very narrow limits in different individuals of the same kind. | 1 | Non-living objects, such as masses of clouds or collections of stones have neither a definite size nor any precise form |
| 2 | A living body is organized of cells, tissues and organs with the division of labour. | 2 | No such organisation exists |
| 3 | Life is an external manifestation of metabolic activities like nutrition, respiration, secretion, circulation, excretion etc. | 3 | None of the metabolic activities is detected in nonliving objects. |
| 4 | The living body increases in bulk by wedging in new particles in between already existing cellular matter. | 4 | Growth may occur occasionally by deposition of particles only on the outer surface of the body |
| 5 | A living body can reproduce its own kind and thus perpetuate its race. | 5 | There is no power to reproduce its own kind |
| 6 | A living body has a definite life cycle. | 6 | No life cycle is observed. The period of duration is infinite and there is no death. |
Question 3. Write briefly about different types of microscopes.
Answer:
Different types of microscopes:
How a Cell can be seen:
Cells got their name from an Englishman named Robert Hooke in the year 1665. He first saw and named “cells” while he was experimenting with a new instrument we now call a “microscope.
“For his experiment, he cut very thin slices from cork. He looked at these slices under a microscope. He saw tiny box-like shapes. These tiny boxes reminded him of the plain small rooms that monks lived in called “cells”. The smallest objects that the unaided human eye can see are about 0.1 mm long.
A magnifying glass can help you to see them more clearly, but they will still look tiny. Cells are not visible under ordinary magnifying glasses.
Smaller cells are easily visible under a light microscope. Light microscopes use a system of lenses to magnify an image. The power of a light microscope is limited by the wavelength of visible light, which is about 500 nm. The most powerful light microscopes can resolve bacteria but not viruses.
Light microscopes (optical microscopes) that are commonly used in schools are of two types – compound microscopes and simple or stereo microscopes (also known as dissecting or binocular microscopes).
Left: Stereo microscope; Center: Compound microscope with a binocular head; Right: Compound microscope with a monocular head is greater resolving power than light microscopes, so we can use them to see even more detail than is visible under a light microscope.
To see anything smaller than 500 nm, you will need an electron microscope Electron microscopes to shoot a high-voltage beam of electrons onto or through an object, which deflects and absorbs some of the electrons.
Resolution is still limited by the wavelength of the electron beam, but this wavelength is much smaller than that of visible light. The most powerful electron microscopes can resolve molecules and even individual atoms.
Some of the specialized types of electron microscopes are – Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), Reflection Electron Microscope (REM), and Scanning Transmission Electron Microscope (STEM).
Question 4. Write, with diagrams, the special features of RBC and nerve cells.
Answer:
Cell-The Unit of an Organism
Your body, as a whole, is one organism. However, many, many parts make up that whole. First, you notice the entire body. Next, you see that the entire body is made up of parts and organs, and each of those organs is made up of a variety of tissues.
And if, as a pathologist does, you examine a magnified sample of one of the human body’s tissues under a microscope, millions of cells become visible.
Yet you can turn up the magnification for an even closer look, Cells contain molecules that are made up of even smaller components called atoms.
Atoms, molecules, cells, tissues, organs, and organ systems are the body’s building blocks. ‘Schleiden and Schwann together proposed the cell theory in 1839.
Cell theory states that “all plants and animals are composed of cells and cellular products.” Thus, the cell is the basic unit of life.
- Salient points of cell theory:
- All living things are composed of cells and their products.
- All cells arise from pre-existing cells.
- AII cells are basically alike in chemical composition and metabolic activities.
- The function of an organism as a whole is the outcome of the activities and interaction of the constituent cells of which the organism is built.
Therefore, all living beings are made up of cells which are the smallest structural and functional unit of the body. Some of them are made up of only one cell and others have many cells.
All living organisms are made up of individual and identifiable cells, whose number, together with their size and type, ultimately defines the structure and functions of an organism.
While the total cell number of lower organisms is often known, it has not yet been defined in higher organisms. In particular, the reported total cell number of a human being is about 37 trillion (one trillion =1,000,000,000,000).
Question 5. Write briefly about the levels of structural organization of organisms. Does the shape of cells remain the same always?
Answer:
Specialised Cells
The table below shows examples of some specialised animal and plant cells, with their functions and special features.
No A cell changes its shape when it undergoes cell division. Human RBC can change its shape when it moves through arteries, veins and capillaries. A cancer-affected cell also undergoes a change in shape of the cell.
Question 6. What are tissues? Name the four principal animal tissues. Write the differences between plant and animal tissues.
Answer:
Levels of organisation:
The Organisation of Cells, Tissues, Organs, Systems and the Organism
From the least complex to the most complex, the organisms are made up of—
- Atom – The smallest piece of matter that still has physical and chemical properties of matter.
- Molecule – The smallest piece of a compound that still has the physical and chemical properties of that substance (e.g., water). The molecule is composed of atoms.
- Cell – The smallest piece of life (some arguments remain about viruses). It is the basic unit of all living beings.
- Tissue – Collection of cells that work together.
- Organ – Collection of tissues that work together.
- Organ System – Collection of organs that work together.
- Organism – Collection of organ systems that makes up a single life form.
Two or more kinds of tissues together form each of our organs, like the heart or lungs. Many organs together form an organ system, like the digestive or respiratory system.
All the organ systems together form an organism, such as a person, dog or blue whale. The body’s organisation goes from cells to tissues to organs to organ systems to a whole working organism. In unicellular (single-celled) organisms, the single cell performs all life functions.
It functions independently. However, multicellular (many-celled) organisms have various levels of organization within them. Individual cells may perform specific functions and also work together for the good of the entire organism.
The cells become dependent on one another. Multicellular organisms have the following 5 levels of organization ranging from simplest to most complex:
Level-1 Cells
Are the basic unit of structure and function in living things. May serve a specific function within the organism.
Examples – are blood cells, nerve cells, bone cells, etc.
Level-2 Tissues
Made up of cells that are similar in structure and function and which work together to perform a specific activity.
Examples – are blood, nervous, bone, etc. Humans have 4 basic tissues: connective, epithelial, muscle, and nervous.
Level-3 Organs
Made up of tissues that work together to perform a specific activity. Examples – heart, brain, skin, etc.
Level-4 Organ Systems
Groups of two or more tissues that work together to perform a specific function for the organism.
The Human body has 11 organ systems – circulatory, digestive, endocrine, excretory (urinary), immune (lymphatic), integumentary, muscular, nervous, reproductive, respiratory, and skeletal.
Level -5 Organisms
Entire living things can carry out all basic life processes. Meaning they can take in materials, release energy from food, release wastes, grow, respond to the environment, and reproduce.
Usually made up of organ systems, but an organism may be made up of only one cell such as bacteria or protists.
Examples – are bacteria, Amoeba, mushrooms, sunflowers, and humans.
The levels of organization in the correct order are:
cells ⇒ tissues⇒ organs ⇒ organ systems ⇒ organisms
Levels of the body from smallest to largest: Atoms, molecules, cells, tissues, organs, and organ systems.
Name the associated processes: gaseous exchange and energy production increase
Question 7. Which cell organelle is primarily responsible for maintaining the shape of plant cells? Jow is a bacterial cell different from an onion peel cell?
Answer:
Processes:
respiration reproduction The shape of a plant cell depends on the volume of water inside the cell. Intake or removal of water from vacuoles depends on the volume of water a plant cell can absorb from the soil. Therefore, vacuoles play important role in the formation of plant bodies.
A bacterial cell is prokaryotic in nature while an onion peel cell is eukaryotic in nature having well-developed cellular organisation.
Question 8. Draw the longitudinal section of mitochondria. What are grana?
Answer:
Inside chloroplastids, the thylakoids are arranged in stacks like piles of coins called grana. Chlorophyll pigments are present in thylakoids.
Question 9. Describe with a diagram the structures and functions of any one animal cell organelle and any one plant cell organelle. Which kind of plastid is more common in: the roots of plants, Flowers and fruits
Answer:
Cell organelles and their structure and function
An organelle is any specialized structure based on the analogy that cells have their cell, especially one for which a specific organelle is just as complex as a multicellular function can be assigned.
As we mentioned organisms have their livers, kidneys, and stomachs earlier, the name means “little organ” and in other organs.
The Three Main Components of any Plant or Animal Cell:
1. Plasma Membrane / Cell Membrane
Structure – It is a bilipid membraneous layer containing proteins and lipids. There are two outer layers of protein and a middle layer of phospholipid. It is called a unit membrane and is semifluid and dynamic in nature.
Function – The cell membrane separates the cell from its external environment, and is selectively permeable (controls what gets in and out). It protects the cell and provides stability.
Proteins are found embedded within the plasma membrane, with some extending all the way through in order to transport materials.
Carbohydrates are attached to proteins and lipids on the outer lipid layer.
2. Cytoplasm
Structure – It is a colourless, semisolid and jelly-like substance composed of main water and found between the cell membrane and nucleus.
The cytoplasm makes up most of the “body” of a cell and is constantly streaming. The transparent fluid part of the cytoplasm is called cytosol.
Function – Organelles are found here and substances like salts may be dissolved in the cytoplasm. It helps in the exchange of materials between cell organelles and is the active site for metabolic processes like sugar, protein and fatty acid synthesis.
3. Nucleus
Structure – The largest organelle in the cell. It is dark and round and is surrounded by a double membrane called the nuclear envelope/ membrane.
In spots, the nuclear envelope fuses to form pores which are selectively permeable. The nucleus contains genetic information (DNA) on special strands called chromosomes.
The colourless dense sap present inside the nucleus is called the nucleoplasm. One or more round bodies present in the nucleoplasm are called nucleoli. A network of dark-staining fibre in the nucleus is called chromatin.
Function – The nucleus is the “control centre” of the cell, for cell metabolism and reproduction. It regulates the cell cycle and is the storehouse of genes.
2. The Organelles found in both Plant and Animal cells:
1. “ER” or Endoplasmic Reticulum
The Endoplasmic Reticulum is a network of membranous canals filled with fluid. They carry materials throughout the cell. The ER is the “transport system” of the cell.
There are two types of ER: rough ER (RER) and smooth ER. (SER)Rough Endoplasmic Reticulum is lined with ribosomes and is rough in appearance and smooth endoplasmic reticulum contains no ribosomes and is smooth in appearance.
ER gives support to the cytoplasm. It forms an intracellular transport system. SER plays a crucial role in detoxifying many poisons and drugs. It also helps in the formation of proteins and lipids.
2. Ribosomes
Ribosomes are small particles which are found individually in the cytoplasm and also line the membranes of the rough endoplasmic reticulum. Ribosomes produce protein. They could be thought of as “factories” in the cell.
3. Golgi Body / Apparatus
Golgi bodies are stacks of flattened membranous sacs, (they look like pancakes). The Golgi Body temporarily stores protein which can then leave the cell via vesicles pinching off from the Golgi.
In plants, the Golgi apparatus is scattered in the cytoplasm and found in the diffused form. These are known as Dictyosomes.
Secretion is the main function of the Golgi complex. It mainly performs the function of packaging.
The material synthesized near the ER is packaged and dispatched to various targets inside and outside the cell through the Golgi apparatus. It is directly involved in the formation of lysosomes.
4. Lysosomes
Lysosomes are small sac-like structures surrounded by a single membrane and containing strong digestive enzymes which when released can break down worn-out organelles or food.
The lysosome is also known as a suicide sac. This help to keep the cell clean by digesting any foreign material and worn-out cell organelles.
5. Mitochondria (Singular = Mitochondrion)
The mitochondria are round “tube-like” organelles that are surrounded by a double membrane, with the inner membrane being highly folded.
The mitochondria are often referred to as the “powerhouse” of the cell. The mitochondria release food energy from food molecules to be used by the cell.
This process is called respiration. Some cells ( muscle cells) require more energy than other cells and so would have many more mitochondria.
6. Vacuoles
Vacuoles are fluid-filled organelles enclosed by a membrane. They can store materials such as food, water, sugar, minerals and waste products.
3. Animal Cell Organelles not found in Plant Cells
1. Cilia and Flagella
Both cilia and flagella are hair-like organelles which extend from the surface of many animal cells. The structure is identical in both, except that flagella are longer and whip-like and cilia are shorter.
There are usually only a few flagella on a cell, while cilia may cover the entire surface of a cell. The function of cilia and flagella include locomotion for one-celled organisms and moving substances over cell surfaces in multi-celled organisms.
4. Organelles and other features found only in Plant Cells
1. Cell Wall
The cell wall is a rigid organelle composed of cellulose lying just outside the cell membrane. The cell wall gives the plant cell its box-like shape. It also protects the cell. The cell wall contains pores which allow materials to pass to and from the cell membrane.
2. Plastids
Plastids are double membrane bound organelles. It is in plastids that plants make and store food. Plastids are found in the cytoplasm and there are two main types:
Leucoplasts – Colourless organelles which store starch or other plant nutrients, (for example – starch stored in a potato).
Chromoplasts – Contain different coloured pigments. The most important type of chromoplast is the chloroplast, which contains the green pigment chlorophyll. This is important in the process of photosynthesis.
3. Central Vacuole
The central vacuole is a large fluid-filled vacuole found in plants.
Question 10. Mention the name of an organism whose body structure does not conform to cell theory What are cytoplasmic organelles? What are A, B and C ? Name the layer which lies outside of the cell membrane in a plant cell.
Answer:
Cells make up A; A makeup B; B make up C; C makes up an organism. The body structure of a virus does not conform to the cell theory.
Some specific living components found in the cytoplasmic matrix of all eukaryotic cells and which are concerned with functions of the cell as a whole are called cytoplasmic organelles,
cells A ⇒B ⇒C ⇒Organism (Tissues) (Organs) (Organ system) Cell wall lies outside the cell membrane in a plant cell.